The present invention generally relates to a dust proof device in an optical pickup device of an optical data recording/reproducing apparatus such as an optical disk recording/reproducing apparatus and, more particularly, to a dust-tight device in an optical pickup device which prevents intrusion of external dust.
A prior art dust-proof device for an optical pickup device has been disclosed, for example, in Japanese patent un-examined publication No. JP-A-59-112447 filed on Dec. 18, 1982 by AKAI DENKI K.K. in Japan, wherein, for the purpose of preventing dust from invading through a gap between the inner periphery of a light-beam passage aperture and the outer periphery of an objective lens into the interior of the optical pickup device, a dust passage route is made long with a complicated structure to give the dust a long detour and minimize the possibility of the dust invasion.
The structure of the optical pickup device will be explained by referring to FIG. 1. The illustrated optical pickup device includes an optical system and a driving mechanism. The optical system includes an objective lens 1, photoelectric elements such as a light-emitting element 15 (e.g., a semiconductor laser element) and a light-receiving element 16 (e.g., a photodiode), a beam splitter 17, and a tracking mirror 14. The driving mechanism includes a coil 3, permanent magnets 5a and 5b and yokes 4a and 4b to drive the objective lens 1. More specifically, the driving mechanism is provided to move the objective lens 1 in its optical axis direction and focus light on a recording surface of an optical disk 13 by utilizing an electromagnetic force generated based on the mutual action between a coil placed in the magnetic field of the permanent magnets and a current flowing through the coil.
The optical pickup device also includes a casing 20 and a cover 11 which enclose the aforementioned optical system and driving mechanism. More in detail, the cover 11 is provided therein with an opening 10 so that a gap is defined between the opening 10 and the objective lens 1 to allow the movement of the objective lens along the opening 10 therein. The objective lens 1 is mounted to the casing 20 by means of thin plate-shaped springs 2a and 2b fixedly mounted on the top and bottom of the objective lens, so that the objective lens can be freely moved vertically (that is, in the optical axis direction) under the influence of the resilient force of the springs with substantially no friction.
The prior art optical pickup device has had such a defect that dust intrudes into the interior of the optical pickup device through a gap between the objective lens 1 and opening 10 during operation of the device and finally adversely affects the mirror 14, photoelectric elements and so on in the optical system incorporated therein, resulting in reduction of its recording and reproducing performances.
With the aforementioned optical pickup device of the aforementioned Japanese Patent Appln. Publication invention, the pickup device has such a structure as to hardly permit the invasion of external dust into the interior of the pickup. However, since there still exists a passage permitting the invasion of external dust into the pickup interior, it cannot be avoided that the external dust enters into the pickup interior from a gap between the inner periphery of an aperture for passage of a light beam and the outer periphery of the objective lens via a curved path.
When a moving part is provided with a cylindrical member for the purpose of making complicated the path for dust to be guided to the interior as in the prior art pickup device, further, this undesirably involves the deterioration of the frequency characteristic of the object lens driver and the reducing of a high-order resonance frequency.
In this way, the prior art optical pickup device has had such a problem that, though the device can avoid the intrusion of relatively large-sized dust particles with a certain level of dust blocking effect, the device cannot virtually avoid the intrusion of relatively small-sized dust particles, and the small dust particles reach the interior of the pickup, which disadvantageously results in that the object lens driver is deteriorated in its frequency characteristic and the high-order resonance frequency is lowered.